Re-mobilisation of radionuclides by wildfires and floods forty years after the Chernobyl nuclear disaster in Ukraine

On 26 April 1986, an explosion and fire at Reactor 4 of the Chernobyl Nuclear Power Plant released substantial quantities of radionuclides into the environment. The accident caused extensive contamination in the vicinity of the plant, while atmospheric transport dispersed radioactive material across parts of the Northern Hemisphere, resulting in fallout beyond Ukraine, including elsewhere in Europe, North Africa and East Asia.

Firefighters, plant personnel and emergency response forces undertook urgent operations to suppress the fire and limit further releases. Many responders received severe radiation exposures, and some died as a result. Authorities evacuated the nearby city of Pripyat and other settlements, subsequently establishing the Chernobyl Exclusion Zone (CEZ), where access and land use remain restricted. Over subsequent decades, technical and environmental management measures have sought to limit the redistribution of residual contamination. Nevertheless, wildfires and flooding remain potential pathways for radionuclide remobilisation, and changes in climate-related hazards may affect the frequency or severity of such events.

This article assesses the potential consequences of wildfire- and flood-driven radionuclide remobilisation for Ukraine and neighbouring countries. It considers atmospheric dispersion and downstream transport through water systems, with particular attention to possible implications for public health, environmental security, military personnel and operational planning. It also examines how actual or perceived contamination risks could be exploited for coercive purposes, including through deniable hybrid activities.

The article first reviews the 1986 accident and the geographic characteristics of the affected area, including the CEZ. It then examines projected climatic changes in Ukraine and the land-cover characteristics relevant to wildfire and flood risk. The analysis focuses on two persistent radionuclides associated with the accident – caesium-137 (¹³⁷Cs) and strontium-90 (⁹⁰Sr) – and evaluates the mechanisms by which wildfire and flooding may remobilise them, drawing on measurements and modelling of past events. Finally, it considers potential health impacts and the implications of future climate-related hazards for contamination management and security planning.